1. Field of the Invention
The present invention relates to a multilayer filter including a plurality of resonators that include loop-shaped inductors and capacitor electrodes.
2. Description of the Related Art
Conventionally, high frequency bandpass filters suitable for miniaturization and low cost manufacturing are each formed by providing a plurality of LC resonators in a multilayer body in which dielectric layers and electrode layers are stacked on top of each other.
Such multilayer bandpass filters are disclosed in Japanese Unexamined Patent Application Publication No. 2006-067221 and International Publication WO 2007/119356.
Japanese Unexamined Patent Application Publication No. 2006-067221 discloses a three-stage multilayer filter in which resonators in the first stage and the third stage are jump-coupled with a coupling capacitor C3, as illustrated in FIG. 1 of Japanese Unexamined Patent Application Publication No. 2006-067221. As illustrated in FIG. 3 of Japanese Unexamined Patent Application Publication No. 2006-067221, the jump-coupling capacitor C3 is formed by arranging an electrode pattern 151 that forms an inductor L1 and an electrode pattern 153 that forms an inductor L3 so as to face an electrode pattern 161.
However, in the structure described in Japanese Unexamined Patent Application Publication No. 2006-067221, the electrode pattern 161 also faces an electrode pattern 152 that forms an inductor L2. Thus, unwanted parasitic capacitance is generated between the electrode pattern 161 and the electrode pattern 152. This poses a problem of Q deterioration in the filter and worsening attenuation characteristics.
On the other hand, International Publication WO 2007/119356 discloses a structure that reduces parasitic capacitance between an electrode pattern of a jump-coupling capacitor and a capacitance electrode pattern of a LC parallel resonator that is not coupled with the electrode pattern of the jump-coupling capacitor.
FIG. 1 illustrates a structure of one of multilayer bandpass filters disclosed in International Publication Pamphlet No. WO 2007/119356. In the multilayer bandpass filter illustrated in FIG. 1, a multilayered body includes a ground electrode forming layer 601, a capacitor electrode forming layer 302, an input-output electrode forming layer 303, a line electrode forming layer 304, and an outer layer 305. On the input-output electrode forming layer 303, there are provided input/output electrodes 621 and 622 as well as an inter input-output capacitor electrode (electrode pattern of a jump-coupling capacitor) 160. The inter input-output capacitor electrode 160 disposed between input and output capacitively couples between the input/output electrodes 621 and 622 by creating capacitance between two input/output electrodes 621 and 622. Capacitor electrodes 311, 312, and 313 on the capacitor electrode forming layer 302 face a ground electrode 309.
To reduce the parasitic capacitance between the inter input-output capacitor electrode 160 (electrode pattern of a jump-coupling capacitor) and the capacitor electrode 312 of the second stage resonator, the capacitor electrode of the second stage resonator is displaced in a direction parallel to the plane of the multilayered body relative to the capacitor electrodes of the first and third stage resonators.
According to the structure illustrated in FIG. 1, the provision of the loop type inductors is effective in improving the Q characteristic of the LC parallel resonator and improving attenuation characteristics of the filter.
Furthermore, in the structure illustrated in FIG. 1, the capacitor electrode of the second stage resonator does not overlap with the jump-coupling capacitor electrode when viewed in a stacking direction of dielectric layers. Thus, the parasitic capacitance therebetween can be reduced.
However, in the structure illustrated in International Publication WO 2007/119356, LC parallel resonators are arranged in a row such that loop planes of all the LC parallel resonators are parallel to each other when including three or more stages of LC parallel resonators. Accordingly, electromagnetic coupling between two inductor electrodes of adjacent LC parallel resonators can be adjusted. However, there is a problem that such an adjustment (setting) is hardly possible between an inductor electrode of an input stage LC parallel resonator and an inductor electrode of an output stage LC parallel resonator. Accordingly, there is a problem that the degree of freedom in adjusting (setting) a filter's attenuation characteristics (particularly positions and bands of attenuation poles) is low.